Conventionally, various methods for manufacturing a piezoelectric thin film obtained by doping in aluminum nitride and a small amount of another element have been proposed. For example, Patent Document 1 described below discloses a reaction sputtering method in which aluminum, and gallium, indium or scandium are reacted with nitrogen in an inert gas atmosphere. Patent Document 1 describes that the polarization direction is inverted by supplying, together with nitrogen, oxygen in a ratio of 0.8 mol % or more and 3.2 mol % or less.
In addition, Patent Document 2 described below discloses an aluminum nitride piezoelectric thin film having a Sc content of 0.5 to 50 at %.
Patent Document 1: JP 2009-149953 A
Patent Document 2: JP 2011-15148 A